The present invention relates to an intermediate for V-28-3M useful as a fungicide, a process for producing it and a process for purifying V-28-3M through the intermediate.
V-28-3M has a high fungicidal activity and a low toxicity. In a previously known method for the purification of V-28-3M in the form of a crude precipitate thereof, after an acid amide or urea is added to an aqueous solution thereof or a solution thereof in a water containing solvent, an insoluble material is removed and an alkali is added to the supernatant to precipitate V-28-3M [Japanese Patent Unexamined Published Application No.5-59084](hereinafter referred to as JP-Kokai 5-59084). However, although the purity of V-28-3M was increased, the crystallization thereof was difficult in this method, and for the further purification, only reversed phase HPLC or counter current distribution method could be employed [Japanese Patent Publication for Opposition Purpose No.4-53878 (hereinafter referred to as JP-Kokai 4-53878)].
In the reversed phase HPLC or counter current distribution method for the high purification, the cost of the purification of the intended product is high because an extremely large amount of the solvent is required for the purification and the quantity of the crude product to be treated each time is only small. Further, the increase in the scale of the laboratory is difficult. Thus, this method is industrially not preferred.
V-28-3M is easily soluble in dimethyl sulfoxide or dimethylformamide, but it is generally difficult to crystallize it from such a polar solvent in which it is highly soluble. Also, although V-28-3M is easily soluble in a water containing solvent such as an aqueous methanol solution, the crystallization thereof from such a solvent is difficult. Methods of recovering V-28-3M from a solution thereof in such a polar solvent in the prior art include a method wherein an extremely large amount of water, for example, 20 parts by volume per part by volume of the solution, is added to the solution, taking advantage of the fact that V-28-3M is practically insoluble in water, or a method wherein an alkali is added to the solution to precipitate V-28-3M at a pH of 12 or above (JP-Kokai 5-59084). However, the precipitate thus obtained could not be crystallized and, therefore, the purity thereof did not reach to the level of that obatined by the HPLC purification method.